For providing addition curing type silicone adhesives which are bondable to a variety of substrates, attempts were made to add tackifiers (or adhesion agents) to curable silicone resins so that the resin might become more adhesive. For example, JP-B 21026/1978 corresponding to U.S. Pat. No. 3,699,072 discloses an addition curing type silicone rubber composition comprising an organohydrogensiloxane having alkoxysilyl groups, and JP-B 13508/1978 corresponding to U.S. Pat. No. 4,077,943 discloses an addition curing type silicone rubber composition comprising an organohydrogensiloxane having epoxy groups.
The prior art addition curing type silicone adhesives, however, are difficultly self-bondable to some substrates, especially resins. Primers must be applied before the silicone adhesives can be bonded. Such difficultly bondable resins are polycarbonates and polyphenylene sulfites. Nowadays, there is an increasing demand for addition curing type silicone adhesives capable of self-bonding to such resins.
As prior art approaches for producing addition curing type silicone adhesives capable of self-bonding to difficultly bondable resins, the addition of nitrogen compounds is known from JP-B 147963/1977. Also developed was a technique of using alkoxysilanes as a tackifier and adding organic tin compounds, organic titanium compounds or organic aluminum compounds as a hydrolytic catalyst.
These techniques, however, are not satisfactory since they can affect the curing of addition curing type silicone adhesives. More particularly, when nitrogen compounds are added to the addition curing type silicone adhesives, these compounds significantly inhibit the catalysis of platinum atom serving as the addition reaction catalyst, resulting in unstable curing. When organic tin compounds, organic titanium compounds or organic aluminum compounds are added, these compounds can deactivate organohydrogensiloxanes in the addition curing type silicone adhesives and act to cleave siloxane bonds in the silicone polymers at elevated temperatures, causing to reduce the heat resistance of the cured composition.